Improvements in Water Treatment for Once-Through Reactor Cooling

Treatment of natural water which has been partly coagulated and settled with minute quantities of any of several new high-molecular-weight organic polymers permits increased flow through modified rapid sand filters. Polymer materials used include acrylamides, polysaccharides, carboxymethylcellulose derivatives, alginates, and carrageenan, among others. The amounts of these materials needed for effective conditioning of the filters are extremely small, dosages ranging at the present time from 0.002 to 0.030 ppm (0.0001 to 0.0015 grains per gal of water). Maximum efficiency is ordinarily obtained by addition of these chemicals to the filter influent flume or directly to the filter gullet. The type of filter system which benefits most from the use of conditioning polymers is a modification of a rapid sand filter. A filter bed composed of 12 in. of gravel, 3 to 6 in. of sand, and 24 to 27 in. of anthracite filter material has given maximum efficiency at Hanford. Sensitive instrumentation is important, and measurement of minute turbidity concentrations is necessary to control film formation in the reactor. At Hanford a light scattering microphotometer has been adapted to measure routinely turbidities in the range 0.001 to 0.010 ppm in the treated water. Increases in water plant capacity and savings in cost have been significant at Hanford with the use of filter conditioning. Total flows through the filters can be 200 per cent greater with filter conditioning than with more conventional treatment methods. A capital cost savings of $250,000 was realized at the time the new treatment was started, and annual cost savings of over $200,000 result from the use of this filter conditioning treatment. The quality of the water produced by this treatment is fully as good as that obtained with previous treatments, and control of water quality is more flexible with filter conditioning.